The invention relates generally to turbomachines and more specifically to a fixture and a method for mounting articulated turbine buckets in axial entry slots of rotor wheels of the turbomachines.
Rotors for turbomachines are often machined from large forgings. Rotor wheels cut from the forgings are often slotted to accept the roots of turbomachine buckets for mounting. As the demand for greater turbomachine output and more efficient turbomachine performance continues to increase, larger and more articulated turbomachine buckets are being placed into service.
The foregoing factors are of particular importance in relation to last-stage steam turbine buckets having improved aerodynamic, thermodynamic and mechanical properties. Last-stage buckets for turbines have for some time been the subject of substantial developmental work. It is highly desirable to optimize the performance of these last-stage buckets to reduce aerodynamic losses and to improve the thermodynamic performance of the turbine. Last-stage buckets are exposed to a wide range of flows, loads and strong dynamic forces. Factors that affect the final bucket profile design include the active length of the bucket, the pitch diameter and the high operating speed in both supersonic and subsonic flow regions. Damping and bucket fatigue are factors which must also be considered in the mechanical design of the bucket and its profile. These mechanical and dynamic response properties of the buckets, as well as others, such as aero-thermodynamic properties or material selection, all influence the optimum bucket profile. The last-stage steam turbine buckets require, therefore, a precisely defined bucket profile for optimal performance with minimal losses over a wide operating range. The bucket may often include a complex blade geometry with overhang.
Adjacent turbine buckets on a rotor wheel are typically connected together by some form of cover bands or shroud bands around the periphery to confine the working fluid within a well-defined path and to increase the rigidity of the buckets. The interlocking shrouds may often present interferences in assembling buckets on the rotor wheel. Inner platforms for the buckets may include tied-in edges, which also may interfere with assembly on the rotor wheel.
Accordingly, it would be desirable to provide equipment and methods for facilitating loading of articulated buckets onto rotor wheels for turbomachines.